The power which can be delivered by an internal combustion engine is limited by the rate at which it can take in air, combine it with fuel and reject the products. A concern, then, arises with effective breathing (i.e., taking in sufficient air) for high engine load conditions. Further, with a strong emphasis on increasing fuel economy and decreasing certain emissions in the exhaust, the operation of the internal combustion engines under light and medium load conditions is also critical, where the way in which the breathing is accomplished is important. Thus, an automotive internal combustion engine can be considered as a multiapplication machine, which requires variable design considerations in order to achieve the optimum performance throughout its wide range of operating speeds and loads.
The inlet conduit to each cylinder, including the intake valve and throat region, is one of the most important areas influencing the engine's volumetric efficiency and combustion burn rate. For high load conditions, if the inlet conduit is correctly designed, it will reduce intercyclic combustion variation through high gas velocities, tumble fluid motion during the cylinder filling process and, hence, higher turbulent intensity with improvement in exhaust gas recirculation (EGR) tolerance, specific fuel consumption and specific power output. The term tumble is used herein to refer to spin in the generally vertical direction in the cylinder, and is used in high flow rate situations.
For reasons of increased burn rate at low speed, low load engine conditions, it is desirable to promote some type of in-cylinder fluid motion. This in-cylinder fluid motion (in-cylinder flow field), the conventional swirl rotation around the cylinder axis (horizontal swirl) generates intake fluid motion to extend the lean capability (improved lean burn capability by having a high air/fuel ratio) of the engine while still maintaining its integrity at full load performance.
Some prior art engine intake configurations have addressed the concerns with adequate swirl in the cylinder at low to moderate engine load conditions by placing vanes in the fluid stream in the vicinity of the intake port. However, these vanes at high load conditions then act to partially block the flow path and restrict the amount of fluid that can flow into the cylinder, thus limiting the maximum power. Further, the vanes will still direct the fluid flow to create swirl rather than a tumble flow field in the cylinder for these high load engine operating conditions.
As used herein, the reference to fluid flow in the intake system can mean just air or an air/fuel mixture depending upon where the fuel is injected into the air stream. The point at which the fuel is injected into the intake system is not directly relevant to the present invention.